The concept of shadow masks for use in television tubes is well known in the art. Typically, a shadow mask having small openings is located in a television tube and acts as guide for the electron beams. Because the shadow mask undergoes a substantial increase in temperature during operation of the television, the shadow mask material expands in accordance with the coefficient of thermal expansion of the mask material, and the increase in temperature. As the shadow mask is used as a guide for electron beams that impinge on the phosphor dots on the glass plate, it is necessary to maintain the proper relationship of the shadow mask to the glass plate even though the temperature of the televisions tube increases during operation of the television. Unfortunately, the glass where the phosphor regions are located has a lower coefficient of thermal expansion than the shadow mask, which can result in misalignment of the shadow mask and the glass. One of the prior art methods of minimizing problems produced by the differences in the thermal expansion rates of the glass and the shadow mask, is to make a shadow mask of a metal which has a coefficient of thermal expansion on the order of the glass. One such commonly used material is a nickel-iron alloy known as an INVAR.TM. alloy. INVAR.TM. alloys can be produced to have a coefficient of thermal expansion on the same order as the glass, thus minimizing the effects of misalignment. One of the drawbacks in the use of Invar alloys is that the Invar alloys are generally more expensive than the conventional steel alloys and make the shadow mask more costly.
The present invention provides a composite shadow mask material formed of bands of a first metal and a sheet of a second metal. The metals are cold rolled together under sufficient pressure so as to form a unitary shadow mask material. The bands of the first metal are made from an alloy having a coefficient of thermal expansion on the order of the glass inside the television tube, and the second metal is made from less costly alloys which have a higher coefficient of thermal expansion. The composite material utilizes the bands of the first metal to form a support to restrain the thermal expansion of the second metal so that the alignment of the shadow mask and the glass plate can be maintained during operation of the television tube.